The long term objective of the present proposalis to identify the vasomotive substances that initiate blood flow regulation of the inner retinal vessels in the normal retina, and to determine the change in concentration of such substances that accompany exposure of the retina to elevated glucose levels. In the eye of anesthetized cat, intraretinal PO2 or pH will be measured by microelectrodes while blood flow is simultaneously measured by laser Doppler velocimetry (LDV). To determine whether O2, CO2, or pH are stimuli for blood flow change we will microinject dissolved O2, CO2, or pH pulses near a retinal vessel in the dark, while monitoring blood flow. We will also determine whether such injections affect blood flow during the vessel's response to light, and whether such changes follow the light titrations for intra- retinal PO2 and pH. We will further explore the possibility of a casual relationship between PO2 and blood flow by determining whether blood flow shows the kinetic complexities to impulsive light flashes found for intraretinal PO2. We will measure cone photoreceptor O2 consumption to light in vitro, and in vivo in the monkey macula while simultaneously measuring blood flow from macular vessels. We will explore the origins of two novel rod photoreceptor O2 consumption changes to light in vitro by ionic substitution experiments. In isolated RPE-choroid preparations, using direct pH measurement we will localize proton active transport systems inferred from RPE O2 consumption determinations, thus exploring a role for the RPE in maintaining the pH balance of the retina. We will further determine whether hyperglycemia reduces RPE O2 consumption in vivo, as observed in vitro, and whether such changes influence intraretinal pH in vivo. Such changes would be most important if pH change is found to induce retinal vasomotion. Lastly, we will measure light-induced changes in O2 consumption from isolated rods and cones, simultaneously with measurement of photoreceptor dark and photocurrents. The proposed experiments will provide information on the basic mechanisms of retinal metabolism and blood flow regulation, and will be relevant to the changes in vasomotion observed in diabetic retinopathy.